1. Field of the Invention
The present invention relates, in general, to a stent that is inserted into a hollow tubular organ such as a bile duct to relieve narrowing of the hollow tubular organ, for instance, on an anastomotic area of the intrahepatic bile duct of a liver transplant patient and, more particularly, to a double-tube type stent having a dual protection structure in which a silicon coating layer is formed on the outer surface of a hollow cylindrical body woven with a superelastic shape-memory-alloy wire using a silicon solution, in which a polytetrafluoroethylene (PTFE) tube is fitted around the cylindrical body having the silicon coating layer leaving a gap therebetween, thereby providing maximum durability, long-term usability and safe removal with respect to the hollow tubular organ.
2. Description of the Related Art
Generally, when a hollow tubular organ, for instance a bile duct, on an anastomotic area of the intrahepatic bile duct of a liver transplant patient, is narrowed, causing a chance of blocking a flow of bile, a request is made to improve the flow of bile.
This improvement of the flow of bile has been mainly accomplished by relieving the narrowing of the bile duct using a stent.
In detail, as illustrated in FIG. 1, the stent 1 which is used is made by weaving a superelastic shape-memory-alloy wire so as to be crossed and thereby form a hollow cylindrical body 3 having a plurality of rhombic spaces 2.
At this time, the stent 1 is used to smoothly guide the flow of bile after a silicon coating layer is formed or after it is covered with a polytetrafluoroethylene (PTFE) tube.
When the silicon coating layer is formed on the stent 1, the silicon coating layer has a lubricating characteristic, and thus smoothly guides the bile in the bile duct. However, the silicon coating layer reduces flexibility, and thus makes it difficult to maintain the stent in the bile duct for a long time.
Further, due to the strongly acidic environment inside the bile duct, the silicon coating layer is dissolved, reducing durability. For this reason, in the case of the stent having such a silicon coating layer, the stent must be typically changed out approximately every three months.
In the case in which the stent is covered with the PTFE tube, the stent is maintainable in the bile duct for a long time due to flexibility of the PTFE tube. Nevertheless, the PTFE tube does not come into contact with the stent, and fails to be firmly fixed to the stent. Accordingly, the PTFE tube brings about inconvenient use, and fails to effectively guide the bile.
More specifically, the PTFE tube is fixed to the stent in such manner that upper and lower ends thereof are tied with a thread. However, since the thread is directly tied to the stent, it does not maintain a firmly tied state due to sliding, or the like.
Moreover, in the case in which only the silicon coating layer is formed on the stent 1, or in which only the PTFE tube is covered on the stent 1, a lesion area of the bile duct cannot be prevented from protruding through the rhombic spaces 2 formed on the outer surface of the stent 1.
In other words, since only one of the silicon coating layer and the PTFE tube has low resistance, it cannot prevent the lesion area of the bile duct from protruding, particularly, from protruding through the rhombic spaces 2 formed on the outer surface of the stent 1. Thus, bleeding occurs through the protruding lesion area of the bile duct. When the stent is to be removed, it is impossible to do so without cutting off the protruding lesion area of the bile duct.